Squeezable wave guide for line stretching



Feb. 27, 1951 M. w. P. STRANDBERG SQUEEZABLE WAVE GUIDE FOR LINE STRETCHING Filed June 14, 1945 lNVENTOR MALCOM W F? STRANDBERG ATTORNEY Patented Feb. 27, 1951 SQUEEZABLE WAVE GUIDE FOR LINE STRETCHING Malcom W. P. Strandberg, Cambridge, Mass, as-

signor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application June 14, 1945, Serial No. 599,503

4 Claims.

This invention relates to waveguides and particularly those whose effective length may be altered by changing a cross sectional dimension.

It is an object of this invention to provide a waveguide whose efiective electrical length may be altered by changing a cross sectional dimension.

It is a further object of this invention to provide a Waveguide whose electrical length may be varied while the mechanical length remains unchanged.

It is a further object of this invention to provide a Waveguide with a means for changing a cross sectional dimension of the guide to effectively alter the electrical length.

Other and further objects will appear during the course of the following description.

In high frequency apparatus it is often desirable to have a line whose electrical length may be varied. Uses of such a line are disclosed in patent application of James L. Lawson, No. 492,062, filed June 24, 1943, Where it is shown that the electrical length of the line connecting the high frequency source of energy with the remainder of the radio frequency system may be adjusted to minimize the losses .of the received energy. Again in a bolometer where the measuring probe is moved longitudinally in a transmission line slot to locate the maximum and minimum position of the standing waves along the line, it has been found that error is introduced due to change in the position of the probe. A transmission line of adjustable electrical length permits change of the longitudinal position of the standing waves along a line with reference to the probe. This allows the probe to remain fixed in position and thus eliminate the error due to movement of the probe.

Lines whose electrical length may be altered by varying the mechanical length are known in the art. Such lines have the inherent disadvantage of requiring excessive space for adjustment over their electrical range, particularly in the lower wave lengths. Furthermore, provision for such adjustment involves the use of sliding joints with the accompanying losses. The instant invention eliminates such disadvantages, since here the only dimension change necessary is in the cross section.

The relationship between the wavelength in a rectangular guide, the wavelength in air, and the effective width may be represented by the following formula;

where Ag=wave length in the guide,

\=wave length in air, and

b=width of guide in the direction normal to the electric vector.

Thus it can be seen that Ag is a function of the guide width b, and as 1) increases Ag decreases. The nearer 21) becomes in value to A (the nearer cut-off the guide is made) the more rapid the.

variation.

A variation in the b dimension of a rectangular guide may be accomplished by longitudinally slotting the middle portions of the two sides perpendicular to the electric vector. Placing the slots in the sides perpendicular to the electric vector prevents any radiation due to the electric field; and having the slots extend longitudinally in the middle of these sides prevents any radiation due to current coupling the slots. The slots must therefore be in the center of planes perpendicular to the electric vector and extend longitudinally of the guide length.

The slots should also be several wavelengths long. This permits a gradual change of the b dimension to prevent a mismatch, and necessitates only a small change in the b dimension to effect a large change in the electricallength of the wave guide. lengthened 10% over 10 wavelengths the wave guide will be electrically shortened by one wavelength.

Reference is now had to the figure in the accompanying drawing, where an embodiment of the invention is disclosed.

A section of rectangular waveguide H is provided with a longitudinally extending slot 12 in i preferably each of the wider opposing walls. The

slots are cut in the middle of the walls of the guide which are perpendicular to the direction of the electric vector of the oscillations in the guide so that an electric field will not appear across the slot and propagation along the guide For example, if Ag is I,

of the oscillatory energy in question will not be appreciably impeded. A clamping structure I3 provided with a screw thread adjustment [4 is mounted on the wave guide in the neighborhood of the slot in such a way that the width of the slot may be adjusted, with a resulting variation in the spacing of the narrower sides of the waveguide I5 and IS. A plate I! is provided between adjustment screw l4 and the adjacent side of the guide to distribute the clamping pressure over a wider area. The resiliency of the waveguide operates against the pressure of the clamping structure so that any adjustment set by the clamping structure less than the normal width of the guide will hold well. It is to be understood, however, that the squeezable portion of the guide may be permanently deformed or shaped to be normally narrower than the rest of the guide, thus bringing the width closer to the cut-off value and making the electrical length more sensitive to changes in the width of the guide. In this form it is necessary to have adjustment screw I4 and the opposing arm of clamping structure [3 mechanically secured to the corresponding guide walls to move these walls apart as the clamping screw moves outwardly.

To vary the electrical length of this guide section, it is merely necessary to vary the spacing between sides 15 and I6 in the vicinity of slot l2 by turning adjustment screw knurled knob. Adjustments in electrical length of more than a half wave length may be obtained by this method. Greater ranges of adjustment may be obtained by providing a plurality of slots and associated dimension varying structure longitudinally spaced along the guide. It is thus apparent that the cross-sectional area of the wave guide or dielectric channel is variable in its b dimension, which is perpendicular to the electric vector of the wave passing through the guide.

Numerous additional applications of the above disclosed principles will occur to those skilled in the art and no attempt has been made to exhaust such possibilities. The scope of the invention is defined in the following claims.

I claim:

1. In combination, a rectangular wave guide [4 with the having a longitudinally extending slot in each of the wider walls, said slot permitting the spacing between the opposing narrower Walls of said wave guide to be varied, a U-shaped member secured to one of said narrower walls, one arm of said U- shaped member extending in spaced relationship to the other of said narrower walls, and means operatively associated with said arm and said other narrower wall and adapted to be operated to vary the spacing therebetween.

2. ,In combination, a rectangular wave guide having a longitudinally extending slot in one of the wider walls, said slot permitting the spacing between the opposing narrower walls of said wave guide to be varied, and a clamping structure positioned on said narrower walls for varying the spacing of said narrower walls.

3. In combination, a rectangular wave guide having a longitudinally extending slot in one of the wider walls, said slot permitting the spacing between the opposing narrower walls of said wave guide to be varied, and a clamping structure mechanically coupled to said narrower walls for varying the spacing of said narrower walls.

4. In combination, a rectangular wave guide having a longitudinally extending slot in each of the wider walls, said slots having a length substantially greater than the wider dimension of said wave guide, said slots permitting the spacing between the opposing narrower walls ofsaid wave guide to be varied without distortion of the wider walls of said wave guide, and means for varying the spacing of said narrower walls.

MALCOM W. P. STRANDBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,669 Bowen Sept. 13, 1938 2,396,044 Fox Mar. 5, 1946 2,403,289 Korman July 2, 1946 FOREIGN PATENTS Number Country Date 503,467 Great Britain Apr. 6, 1939 

